Regenerated cellulose is a robust, cost effective material which would likely be more widely used if inflated structures of regenerated cellulose could be readily produced without the drawbacks of prior art methods of making such products.
Regenerated cellulose, sometimes referred to as semi-synthetics or cellulosics, are well-known in the art. Rayon is made by way of the viscose process which involves reacting cellulose with a concentrated solution of sodium hydroxide to form soda cellulose followed by reacting the soda cellulose with carbon disulfide to form sodium cellulose xanthate. The sodium cellulose xanthate is dissolved in a dilute solution of sodium hydroxide to give a viscose solution which is aged and then extruded through spinerettes into dilute sulfuric acid, which regenerates the cellulose in the form of continuous filaments. Cellulose acetate and triacetate products are produced from a dope of cellulose acetate dissolved in acetone and/or a chlorinated hydrocarbon. Lyocell products are made from cellulose dissolved in N-methylmorpholine N-oxide (NMMO). See U.S. Pat. No. 4,246,221 of McCorsley et al., as well as U.S. Pat. No. 3,508,941 of Johnson. Degradation of the cellulose polymer, reactive chemical species in the dopes, high temperatures, harsh conditions and solvent disposal are significant processing issues with these products, making it extremely difficult to manufacture inflated cellulosic products utilizing conventional cellulosic technology.
Nevertheless, methods of making inflated textile fibers from, for example, viscose rayon, are known in the art. Various methods are reviewed in a 1985 non-wovens symposium paper entitled “The Manufacture, Properties and Uses of Inflated Viscose Rayon Fibers” authored by Woodings et al. U.S. Pat. No. 3,156,605 to Anderer et al. discloses producing inflated rayon fibers from viscose having nitrogen emulsified therein, while GB Patent 244,446 discloses the manufacture of flat ribbon-shaped artificial textile fibers which are more or less hollow from viscose with sodium carbonate or sodium bicarbonate. Also noted is U.S. Pat. No. 5,124,197 of Bernardin et al. entitled “Inflated Cellulosic Fiber Web Possessing Improved Vertical Wicking Properties”. This patent reports that an absorbent web formed from inflated cellulose fibers possesses improved vertical wicking properties compared to a similar web of cellulose fibers. The webs are reported useful for use in forming absorbent products such as diapers and the like.
U.S. Pat. No. 6,808,557 to Holbrey et al. entitled “Cellulose Matrix Encapsulation and Method” discloses a regenerated cellulose with encapsulated active substance such as dyes or magnetic particles within a matrix of regenerated cellulose prepared from an ionic liquid/cellulose solution. The regenerated cellulose has a molecular weight similar to the original cellulose and is prepared substantially free of substituent groups relative to the starting cellulose. The '557 patent notes in Col. 13 that engineered forms containing impregnated additives with enhanced properties and application can be prepared from ionic liquid solution. Specific additives mentioned include bioactive agents, metal complexants, water insoluble dyes, nanoparticles, photonic agents, UV screens, magnetic particles and dispersions of clays. Note also, U.S. patent application Ser. No. 11/087,496; Publication No. US 2005/0288484 to Holbrey et al. entitled “Polymer Dissolution and Blend Formation in Ionic Liquids”, as well as U.S. patent application Ser. No. 10/394,989; Publication No. US 2004/0038031 to Holbrey et al. entitled “Cellulose Matrix Encapsulation and Method”.
Calcium carbonate has been used as a filler for making high strength paper. For example, there is disclosed in U.S. Pat. No. 6,235,150 to Middleton et al. a method for attaining high levels of loading of calcium carbonate fillers in the lumens of naturally-derived wood pulp fibers. The pulp is pretreated with a cationic polymer prior to being impregnated with the filler. Different conditions of pH and temperature are specified depending on whether the filler is a precipitated calcium carbonate filler or a ground calcium carbonate. Another method for providing calcium carbonate into a fibrous matrix involves supplying a precursor and then treating impregnated fibers with carbon dioxide. See U.S. patent application Ser. No. 10/927,890, Publication No. US 2005/0121157 of Doelle et al., as well as U.S. patent application Ser. No. 10/543,191, Publication No. US 2006/0113051 of Dolle. Wood pulp fibers are not amenable to inflation with an effervescing agent such as calcium carbonate due to their porosity.
It has been found in accordance with the present invention that inflated cellulose structures are readily formed from an ionic liquid/cellulose dope which has been impregnated with an effervescing agent and regenerated into the desired structure.